Tuesday, 30 August 2016

Often you could accuse astronomers of being overly fanciful when they invent nicknames for the things they've discovered or the constellations they've assigned. You might even believe that the astronomy society's a less successful branch of alcoholics anonymous. :-) But at times you don't need a lot of fantasy to understand why a certain object was given a certain name. Such is the case with the distant galaxy that's the protagonist of this sketch.

I've taken my new binoscope for a five nights' holiday in the Dolomites, at an elevation of 2000 metres and under a sky of a rare darkness. The goal: hunt the faintest fuzzies! The "tadpole galaxy"(or scientifically UGC10214 or Arp188) is quite faint indeed, being of magnitude 14,4, but it's one of the most spectacular of them all. Most galaxies are round or elliptical but this one has an unusual straight tail that's 280.000 lightyears long. Scientists believe that a smaller and more compact galaxy's come too close and that their mutual gravitational forces slung it around the "tadpole". Gas, dust and millions of stars were torn out of the larger one and formed the striking tail. Over time, the "tadpole" will lose its tail, which will probably contract into dwarf galaxies that accompany their mother. The intruder's not visible on the sketch because it now lies somewhere behind the "tadpole", but it can be seen on high-resolution photos of the Hubble space telescope. My binoscope's quite powerful but certainly not that powerful. Bear in mind that this particular galaxy lies at a distance of a whopping 460 million lightyears and therefore it must be the most distant object that I've observed thusfar.

For those with a keen eye... there's a second galaxy on my sketch, smaller and even fainter. Its scientific denominator's PGC57108, it's of magnitude 15,5 and lies at approximately the same distance. I dare you to find it! :-)

Thursday, 11 August 2016

There are so many planetary nebulae out there that sketching all of them would be close to impossible. As you know, they're dying stars that've just shed their atmosphere into space. When I use the term "just", we're talking about only several thousands of years ago, which is a nanosecond compared to the age of the universe. Their incredibly hot core heats up the resulting gas cloud up to the point that it starts to emit light on its own. Slowly this cloud of gas will expand and dissolve into space whereas the core, the remaining white dwarf star, will cool down and eventually extinguish.

Planetary nebulae are called this way because they truly look a bit like a planet, with their generally round shape. But if you zoom into them, they'll reveal a surprising amount of detail. Gas filaments, structures and different layers give every single planetary nebula a character of its own and make every new one that you observe also a new experience. Yesterday I showed you the "Blue Flash" nebula. Not that far from it you can find this little fellow: the "Glowing Eye" in the tail of the constellation of Aquila, the eagle. With its magnitude of 11,9 it's within reach of most telescopes but due to its tiny size it can be quite tricky to find. For my sketch I used a magnification of 507x, which brought out quite some detail. I could easily see the brighter rim and some filaments of the inner sphere, which does look a bit like an iris. Its central star was also a lot more prominent than the one of NGC6905.

Wednesday, 10 August 2016

NGC6905 is a wonderful planetary nebula in the small but remarkable constellation of Delphinus. Loyal readers of my blog will already have guessed that this nebula is what's left of a dying normal-sized star. The star's nucleus still survives and has turned into an extremely hot white dwarf star with a surface temperature around 150.000°C. In comparison, the temperature on our Sun's surface is only 5.500°C. A white dwarf's a very peculiar kind of star because its size is comparable to that of the Earth whereas its mass is not much different to our Sun's. Needless to say that it's extremely dense and "heavy". Unlike a normal star, no nuclear fusion takes place in it anymore; it's light and energy emission being solely the result of the remaining heat of what was once an active nuclear fusion reactor. With time, this star will therefore slowly cool down and fade until all that's left is a ball of mainly carbon. This cooling process takes a lot of time, many billions of years, and therefore there aren't such carbon balls or "black dwarves" around yet because the universe simply isn't old enough.

This particular white dwarf was clearly visible in my binoscope. But perhaps more interesting for visual astronomers, the star's atmosphere was expelled into space and now forms a rapidly expanding bubble of gas filaments around the white dwarf. Also these filaments were more than evident in the binoscope at a magnification of 285x. Actually, I was amazed at the amount of detail that I was able to make out. This planetary also has two extremely faint "wings" just above and below the main nebula on this sketch. These were difficult to see and I've tried to represent just that. Some people therefore call it a mini-Dumbbell nebula because it does look a bit like a smaller and fainter version of the famous nebula in Vulpecula.

The "Blue Flash" however lies a lot further away from us: 7.500 lightyears compared to 1.300 for the Dumbbell. But I hope that my sketch will encourage you to visit this fainter and more distant planetary as well because it really deserves it.

Wednesday, 3 August 2016

I've already talked about supernovae before, cataclisms that mark the death of a giant star. Nuclear fusion becomes unstable... the star collapses under its own gravity which in turn causes the violent expulsion of the entire star's atmosphere in a matter of seconds. The acute energy release may be as high as 1044 Joules or the entire energy output of the Sun during its whole 10-billion year life! The expelled matter may reach velocities up to 30.000km/s or one tenth of the speed of light!

But as dramatic and spectacular as they appear, the remains of the star fade quickly and after a couple of months all that's left is an incredibly dense core that consist of neutrons. Although perhaps only 10km in diameter,the neutron star's density is 1015 higher than that of normal matter and hence it's incredibly heavy. In some cases it may be heavy enough to continue to collapse under its own gravity until it has become a point. At which stage it becomes a black hole: an object with such a high mass that you'd need to travel faster than light in order to escape from it. That's why we can't observe anything within them because nothing, not even light, travels fast enough to escape.

But supernovae are not just the end. The blast is so strong that heavier elements such as metals are formed and expelled into the universe. So in a sense a supernova feeds the universe with a lot of complex elements which one day may be needed for the creation of planets and... life. And not all's destroyed instantly. Almost 6.000 years ago a vehement supernova lit up 1.400 lightyears from us in the constellation of Cygnus. As far as I'm aware no observation reports from that day exist so we can only speculate how our ancient ancestors stared at the sky in awe when an insignificant star suddenly became brighter than the full Moon. Now, thousands of years later, the remains of that explosion are still visible in a small to medium telescope: the Veil nebula. What I've sketched here is just a part of the eastern region. The total Veil nebula complex is 110 lightyears in diameter, or in our sky this equals 6 full moons, and continues to expand at a breathtaking rate. Gas filaments that mainly consist of oxygen are heated up and ionised by the blastwave of the supernova explosion and start to emit light themselves. Exactly these frail filaments are what makes this nebula so jaw-droppingly lovely to look at and in a big instrument such as my binoscope the spectacle surpasses even the wildest imagination. I just had to share this with you and I sincerely hope that you enjoy it.

Earlier than planned, I'm releasing the second part of my video series about astronomical sketching techniques. In this episode I'm focusing on the sketching of the background stars, something which is often overlooked but which highly contributes to the overall result.

Sketching stars is not just putting dots on paper. In order to make the drawing as accurate as possible you need to master an easy technique which I demonstrate in the video.